Composition dependence of ion transport coefficients in gas mixtures

A simple momentum-transfer theory for the composition dependence of ion mobilities and diffusion coefficients in gas mixtures at arbitrary field strengths is corrected, extended, and compared with a similar theory based on momentum and energy transfer, and with results based on direct solution of the Boltzmann equation by Kihara's method. Final equations are recommended for predicting composition dependences, given only results on ion mobilities and diffusion coefficients in the pure component gases

Incoherent pion photoproduction on the deuteron with polarization observables I: Formal expressions

Formal expressions are developed for the general five-fold differential cross section of incoherent $\pi$-photoproduction on the deuteron including beam and target polarization. The polarization observables of the cross section are described by various beam, target and beam-target asymmetries for polarized photons and/or polarized deuterons. They are given as bilinear hermitean forms in the reaction matrix elements divided by the unpolarized cross section. In addition, the corresponding observables for the semi-exclusive reaction $\vec d(\vec \gamma,\pi)NN$ are also given.Comment: 11 pages, 1 figur

Polarization observables in π0η\pi^0\eta-photoproduction on the proton

For $\pi^0\eta$-photoproduction on the nucleon formal expressions are developed for the five-fold differential cross section and the recoil polarization including beam and target polarizations. The polarization observables are described by various beam, target and beam-target asymmetries for polarized photons and/or polarized nucleons. They are given as bilinear hermitean forms in the reaction matrix elements divided by the unpolarized cross section. Numerical results for the linear and circular beam asymmetries for $\gamma p\to\pi^0\eta p$ are obtained within an isobar model and are compared with existing data. Predictions are also given for the target asymmetry $T_{11}$, and the beam-target asymmetries $T^c_{10}$ and $T^c_{11}$ for circularly polarized photons.Comment: 19 pages, 8 figure

A historic jet-emission minimum reveals hidden spectral features in 3C 273

Aims. The aim of this work is to identify and study spectral features in the quasar 3C 273 usually blended by its strong jet emission. Method. A historic minimum in the sub-millimetre emission of 3C 273 triggered coordinated multi-wavelength observations in June 2004. X-ray observations from the INTEGRAL, XMM-Newton and RXTE satellites are complemented by ground-based optical, infrared, millimetre and radio observations. The overall spectrum is used to model the infrared and X-ray spectral components. Results. Three thermal dust emission components are identified in the infrared. The dust emission on scales from 1 pc to several kpc is comparable to that of other quasars, as expected by AGN unification schemes. The observed weakness of the X-ray emission supports the hypothesis of a synchrotron self-Compton origin for the jet component. There is a clear soft-excess and we find evidence for a very broad iron line which could be emitted in a disk around a Kerr black hole. Other signatures of a Seyfert-like X-ray component are not detected.Comment: 4 pages. Accepted for publication in A&A Letter

Comparison of E-ink and OLED screens as train seat displays : a user study

This study was designed to provide an evaluation of two types of train seat displays (OLED and E-ink), from a user-centred perspective. Numerous factors influence the decisions on which display to use, such as costs or energy use. It is also important to consider human factors aspects like readability and user preferences. To provide some real-world insights into these issues we designed a pilot study to compare both displays. Participants were asked to give their impressions and respond to questions during a semi-structured interview process, when they were presented with both displays. Results show that participants favour the OLED display overall as it is easily noticeable in different light conditions. However, some aspects of the E-ink are preferred: it is easier to read and understand. We conclude that research with real users is extremely important when designing and defining hardware to be used during the implementation of intelligent transport systems

Consequences of fish for cladoceran, water beetle and macrophyte communities in a farmland pond landscape: implications for conservation

Traditionally, fish have been neglected in pond ecology and conservation studies and it has frequently been assumed that they have a detrimental impact on pond biodiversity and ecosystem function. In order to assess the consequences of fish for pond biodiversity and ecosystem structure we sampled a set of 40 small farmland ponds (20 with and 20 without fish) in eastern England and compared their water chemistry as well as assemblage characteristics (abundance, diversity, species composition) for three biological groups: cladocerans (zooplankton), water beetles and macrophytes. Water depth was significantly greater in fish ponds, while pond bottom oxygen levels and pH were significantly higher in the ponds without fish. The presence of fish significantly reduced the abundance of macrophytes and altered the community composition of cladocerans and macrophytes, but had no detectable influence on water beetles. Variation partitioning using environmental and spatial variables, indicated that all three biological groups were spatially structured. The inclusion of fish, however, reduced the importance attributed to space in the case of both cladocerans and macrophytes, suggesting that space effects for these two groups were at least partly the result of a spatially structured predator (i.e.fish). In most cases fish did not have an effect on cladoceran and water beetle alpha diversity (number of species, Shannon's and Simpson's index), although the opposite was true for macrophytes. Nevertheless, at the landscape level, gamma diversity (i.e.total number of species) was enhanced for all three biological groups. Our results suggest that fish, at least small, typical, pond-associated species, are an important component of heterogeneity in farmland pond networks, thereby increasing landscape-scale diversity across several faunal and floral elements. Consequently, we propose that fish should be more fully included in future pond biodiversity surveys and conservation strategies

30 years of multi-wavelength observations of 3C 273

We present a wide multi-wavelength database of most observations of the quasar 3C 273 obtained during the last 30 years. This database is the most complete set of observations available for an active galactic nucleus (AGN). It contains nearly 20'000 observations grouped together into 70 light curves covering 16 orders of magnitude in frequency from the radio to the gamma-ray domain. The database is constituted of many previously unpublished observations and of most publicly available data gathered in the literature and on the World Wide Web (WWW). It is complete to the best of our knowledge, except in the optical (UBV) domain where we chose not to add all observations from the literature. In addition to the photometric data, we present the spectra of 3C 273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the X-ray domain, we used the spectral fit parameters from the literature to construct the light curves. Apart from describing the data, we show the most representative light curves and the average spectrum of 3C 273. The database is available on the WWW in a homogeneous and clear form and we wish to update it regularly by adding new observations.Comment: 12 pages, 6 figures, to be published in A&AS, data available at: http://obswww.unige.ch/3c273

Understanding Search Trees via Statistical Physics

We study the random m-ary search tree model (where m stands for the number of branches of a search tree), an important problem for data storage in computer science, using a variety of statistical physics techniques that allow us to obtain exact asymptotic results. In particular, we show that the probability distributions of extreme observables associated with a random search tree such as the height and the balanced height of a tree have a traveling front structure. In addition, the variance of the number of nodes needed to store a data string of a given size N is shown to undergo a striking phase transition at a critical value of the branching ratio m_c=26. We identify the mechanism of this phase transition, show that it is generic and occurs in various other problems as well. New results are obtained when each element of the data string is a D-dimensional vector. We show that this problem also has a phase transition at a critical dimension, D_c= \pi/\sin^{-1}(1/\sqrt{8})=8.69363...Comment: 11 pages, 8 .eps figures included. Invited contribution to STATPHYS-22 held at Bangalore (India) in July 2004. To appear in the proceedings of STATPHYS-2

Variability of Quasars at 10 microns

Twenty five low redshift quasars have been monitored for several decades at five near- and mid-infrared wavelengths to detect rapid variations which would indicate that a nonthermal component was present in the "10 micron bump". Such variability has apparently been detected in several radio loud quasars and in the radio quiet quasar PG1535+547. In addition, the structure function of PG1226+023 shows that an apparently periodic component is present in its near-infrared emission.Comment: AAS LaTex, 33 figures in 2 postscript files, AJ, accepte

Polarization observables of the gamma d --> PiNN reaction in the Delta(1232)-resonance region

Polarization observables of the three charge states of the pion for the $\gamma d\to\pi NN$ reaction with polarized photon beam and/or oriented deuteron target are evaluated over the whole $\Delta$(1232)-resonance region adopting a nonrelativistic model based on time-ordered perturbation theory. Results for the $\pi$-meson spectra, linear photon asymmetry, vector and tensor target asymmetries are presented. Particular attention is given, for the first time, to double polarization asymmetries for which we present results for $T_{20}^{\ell}$ and $T_{2\pm 2}^{\ell}$. We found that all other double polarization asymmetries of photon and deuteron target are vanished.Comment: 17 Pages, 8 Figures, accepted for publication in Int. J. Mod. Phys.